ORIGINAL PAPER Morphology, ontogenesis and mechanics of cervical vertebrae in four species of penguins (Aves: Spheniscidae) Geoffrey Guinard • Didier Marchand • Fre ´de ´ric Courant • Michel Gauthier-Clerc • Ce ´line Le Bohec Received: 3 September 2009 / Revised: 10 December 2009 / Accepted: 11 December 2009 Ó Springer-Verlag 2009 Abstract Penguins (Aves: Spheniscidae) are pelagic, flightless seabirds, restricted to the southern hemisphere (Antarctic and sub-Antarctic areas, New Zealand, Australia, and nearby islands, as well as parts of South America and South Africa). They spend much of their life at sea, but return to islands and coasts to breed. Penguins are terrestrial as juveniles and aquatic as adults. To improve hydrody- namics, penguins tuck in their necks while swimming. They thus attain an ‘‘ichthyosaur’’ or ‘‘cetacean’’ body shape: characterised by telescoped cervicals. This mechanism is also used on land, associated with the posture of these birds. Our study of neck structure and cervical vertebrae mor- phology (morphological description, biometry and contour analysis) of the King Penguin (Aptenodytes patagonicus), Gentoo Penguin (Pygoscelis papua), Macaroni Penguin (Eudyptes chrysolophus) and Humboldt Penguin (Sphensi- cus humboldti) shows a highly specialised fitting in adults, which develops during ontogenesis. The growth of penguins proceeds by stages and there are key stages with regard to the design of the neck. Despite a common main structure, some characteristics vary between species. Distribution of cervical vertebrae can be defined by six modules. There are differences in modularity between species and also within species between different ontogenetical phases. Keywords Penguins Á Spheniscidae Á Cervical vertebrae Á Ontogenesis Á Modularity Introduction Penguins are the only birds that have succeeded in col- onising the aquatic environment to such an extent that some species can remain at sea for several months, like A. patagonicus. Their hydrodynamic morphology, which makes propulsion more efficient, especially during ‘‘underwater flight’’, ‘‘imitates’’ that of ichthyosaurs or cetaceans, other aquatic vertebrate colonists of importance. Admittedly, the two latter groups have evolved from a terrestrial ancestor, while penguins have a flying ancestor. In addition, ichthyosaurs and cetaceans have caudal pro- pulsion whereas penguins use their flippers. However, there are essential common features to promote hydrodynamic morphology, such as the tilting of supra-occipital bone Electronic supplementary material The online version of this article (doi:10.1007/s00300-009-0759-2) contains supplementary material, which is available to authorized users. G. Guinard (&) 58 rue des Pe ´joces, 21000 Dijon, France e-mail: geoffrey.guinard@yahoo.fr G. Guinard Á D. Marchand Á F. Courant CNRS UMR 5561, Bioge ´osciences, Universite ´ de Bourgogne, 6 Boulevard Gabriel, 21000 Dijon, France D. Marchand e-mail: Didoux.Marchand@gmail.com F. Courant e-mail: frederic.courant@u-bourgogne.fr D. Marchand 8a Avenue Sainte Claire, 06100 Nice, France F. Courant 6 rue du Midi, 21800 Quetigny, France M. Gauthier-Clerc Á C. Le Bohec Centre d’e ´cologie et physiologie e ´nerge ´tiques, UPR/CNRS 9010, 23 rue Becquerel, 67087 Strasbourg, France e-mail: michel.gauthier-clerc@c-strasbourg.fr C. Le Bohec e-mail: celine.lebohec@c-strasbourg.fr 123 Polar Biol DOI 10.1007/s00300-009-0759-2